The sanitary and domestic paper industry uses a creped paper called cellulose cotton, also tissue paper, in the manufacture of products. The property of this paper to stretch due to its creping is used in embossing it, i.e., to permanently deform the paper at some locations and, in particular, to achieve projections on one side of the sheet.
Regarding sanitary products, the trend of the past years has been to make them softer, more velvety, more attractive while nevertheless preserving or improving their functional features of thickness and strength in particular. The latter features may be affected, whether improved or degraded, by the embossing procedure. Embossing is carried out either on a paper with a high moisture content, that is on a partly moist paper machine, or on low-moisture content paper, that is by transformation into a dry part. The present invention relates to embossing low moisture-content paper.
The most common embossing patterns are repetitive and geometrically based on elements of small cross-sectional protrusions and evincing simple geometric shapes (FIG. 1). One such embodiment is shown in U.S. Pat. No. 3,414,459.
The repeat frequency of the projections of these kind of patterns may be high, the density of the elements ranging from 5 to 60 per cm.sup.2 depending on the application being a paper towel or sanitary paper. The surface of the tops of the elementary protrusions may be less than 1 mm.sup.2. Such patterns affect mainly the properties relating to the sheet thickness on one hand and to its stiffness and strength on the other. These patterns offer a good tradeoff between the desired feature improvements when the semi-finished product is converted into a finished product and industrial operations, in particular, these patterns permit applying adequate embossing intensity.
On the other hand, much research has shown that these so-called technical patterns are hardly visually attractive to the consumer, in particular, when of low density. This negative perception is compounded by their pronounced diffuseness which makes them anonymous.
Solutions for increasing the visual impact of these sanitary products without thereby degrading the basic paper properties already have been elaborated.
One solution consists in printing decorative patterns before or after embossing. This solution offers the advantage of little affecting the embossing contribution and enhancing product visibility. However, it entails the drawback of putting on the market colored and decorated products whereas most consumers prefer solid colors. Moreover, this solution entails additional equipment and sometimes penalizes the efficiency of the production line.
Another solution of the prior art suggests providing embossing patterns enhancing the visual facet besides the predominant technical patterns. The visual patterns are of a repeat frequency much lower than that of the technical patterns and their unit surface is larger by an order of magnitude. FIG. 2 shows a pertinent sample from the disclosure of European Patent No. 265,298 and of U.S. Pat. No. 4,376,671.
The impact of these patterns on the physical paper properties is less. The rigidity and the thickness of the sheet are little modified. Their main advantage is the signature or at least the potential for differentiation which they offer. On the other hand, this major advantage is linked directly to their legibility or visibility.
To achieve the objective of visual attractiveness, two prior approaches may be noted. The first one employs high embossing density to ensure good marking while the second is restricted to patterns allowing good embossing under usual processing conditions. In the prior art, these two approaches perforce have been implemented simultaneously.
The more the appearance is emphasized, the more complex the geometric shapes. This fact entails less marking power on the sheet and the embossing will be less regular. Accordingly, embossing intensity must be raised if the product characteristics are to be controlled to the desired extent. Thereby, the intrinsic defects of this kind of pattern are amplified relative to embossing regularity and hence regularity of the behavior of the sheet both locally and overall. As a result, the product appearance is degraded and the overall embossing procedure suffers with respect to retaining dimensions, speed and more generally efficiency.
This is the explanation of the tradeoff incurred for these patterns between their marking intensity and their use on an industrial scale. This tradeoff is at the cost of legibility, visibility and the expected improvement in the characteristics entailed by processing the semi-finished goods into finished ones. In practice, the choice will be necessarily in favor of the constraints relating to making the sanitary product while pushing the aesthetic constraints into the background.
These patterns may be called "technical-aesthetic" and because of the factors stated above evince a fairly high repeat frequency and a comparatively compact and closed form. They use simple geometric shapes and, where necessary, shapes assembled to constitute an elementary pattern indefinitely repeated in the longitudinal and transverse directions and of which the orientation is constant. Lastly, as regards a pattern made in conformity with the disclosure of European Patent No. 265,298, the constancy of thickness of the lines forming the element contour is noteworthy.
Another solution of the prior art defines a technical pattern beforehand and reserves regularly spaced zones which as a rule will assume geometric shapes by suppressing picots from this pattern. These zones then are either left as such or else they are decorated with an aesthetic pattern. Occasionally, a printed pattern is also used, but if so at the cost of visibility and hence of legibility of the visual pattern component.
The object of these combinations is to control, on the basis of the technical patterns, the functional factors of thickness, strength and softness in the manner of U.S. Pat. No. 4,320,162. This patent relates to combining two double-depth pattern, namely, a first pattern with elements that are mutually fairly well spaced apart and of substantial depth and a second pattern evincing a shallower depth. In the illustration of this patent, the first pattern is arbitrarily taken as a flower while the second is conventionally identified by picots. The essential features described above for the technical-aesthetic patterns, in particular the near-constant orientation of the primary patterns, are retained in such combinations.
None of these solutions allows fully exploiting the potential offered by the aesthetic patterns as regards the final user.
It is known that value systems (with positive or negative values) can be controlled by judiciously using shapes, motions, directions (for example like logos). Moreover, much research has shown a "halo" phenomenon due to an especially positive perception of one product feature by the consumer decreasing or masking elsewhere the perception of any weak points.
It was impossible to apply such principles to embossing patterns in the prior art.
Foremost the reason is that their essential features of freedom, motion, visibility and legibility to a large extent are incompatible with the constraints entailed from the function and production of sanitary products (thickness, uniform behavior of the sheet, product appearance, speed and production efficiency).
This incompatibility will be pronounced the more these essential features are reinforced by the high embossing intensity required to achieve minimum criteria of economic feasibility in view of the low embossing ability of such free patterns.
The object of the invention is to resolve this problem.